1. Field of the Invention
The present invention relates to electrosurgical devices for ablating tissue in a surgical procedure. More specifically, the present invention relates to electrosurgical devices having an improved electrode design.
2. Relevant Technology
An arthroscope is an instrument used to look directly into a surgical site. Typically, the arthroscope utilizes a magnifying lens and coated glass fibers that beam an intense, cool light into the surgical site. A camera attached to the arthroscope allows the surgeon to view the surgical site on a monitor in the operating room. With the arthroscope, the surgeon can look directly into a surgical site, such as a knee or shoulder, to diagnose injury and decide on the best treatment. While viewing the surgical site with the arthroscope, the surgeon can repair an injury using a separate surgical instrument.
The ability to view the surgical site in this manner allows for a minimally invasive procedure. In recent years, arthroscopic surgeries have been developed for surgical procedures that traditionally were once very complicated and time consuming. Many of these surgeries are now performed as outpatient procedures using arthroscopic techniques.
At the beginning of the arthroscopic procedure, the patient receives an anesthetic. After the patient has been sufficiently anesthetized, the surgeon makes a plurality of incisions, known as portals, from the exterior of the body of the patient to the surgical site. Three portals are usually made: a first for the arthroscope, a second for the surgical instrument, and a third to permit fluids to escape from the surgical site. Sterile fluid, e.g., saline solution, is generally introduced by way of the arthroscope through the first portal. The sterile fluid serves among other purposes to expand the area of the surgical site. The introduction of sterile fluid makes it easier to see and work inside the body of the patient at the surgical site.
“Electrosurgical” instruments are commonly used in arthroscopy to ablate and/or coagulate tissue. In electrosurgery, a high-frequency current is applied to an electrode near or touching body tissue. As discussed in further detail below, at lower power levels the high-frequency current can be used to heat tissue through direct conduction, and at higher power levels can be used to form a plasma providing sufficient heat to ablate tissue. The present invention relates to improvements in such electrodes.
The electrosurgical electrode serves as one pole whereby a circuit is completed such that the high-frequency electrical current flows. In “monopolar” electrosurgery the return electrode is a patch placed elsewhere on the patient, so that the circuit is completed by energy being dissipated into the tissue and passing through the patch. In a “bipolar” electrosurgical device, the return electrode is placed in a separate location on the electrosurgical device. Energy leaving the electrode passes through fluids and/or tissue and returns to the return electrode on the electrosurgical device. The improved electrode of the present invention can be used in either monopolar or bipolar electrosurgery.
In both monopolar and bipolar electrosurgery, an electrode transfers energy to the surrounding fluid. The energy can be controlled to simply heat the adjacent tissue or to cut or ablate the tissue. Heating of the tissue is often done to facilitate coagulation, that is, to stop bleeding.
To ablate tissue, larger amounts of energy are applied to the electrode. The electrode generates enough heat to create gas bubbles around the electrode. The gas bubbles have a much higher resistance than tissue or saline solution, which causes the electrode voltage to increase. Given sufficient power the electrode discharges (i.e., an arc is formed). The high voltage current travels through the gas bubbles and creates a plasma discharge over the surface of the electrode. If the electrode is moved sufficiently close to tissue the plasma discharge is effective to ablate the tissue.
The contours and surface area of an electrode are important for controlling where arcing occurs on the electrode and how much power is required to cause a discharge. More specifically, arcing occures preferentially where current density is greatest in the electrode; in general, current density is maximized at sharp edges. Arcing, and thus the ability of the electrode to form an effective ablative tool, can be thus be encouraged by forming electrodes or electrode edges with small surface areas. Typically, sharp edges, that is, members of small surface areas where current density is concentrated, are created on the distal face of an electrode by forming grooves therein or assembling small-diameter wires to the body of the electrode so that the wires form edges of small surface area. See commonly-assigned U.S. Pat. Nos. 7,244,256 and 7,150,746 to the present inventors.
An important aspect of the design of an electrode for electrosurgery is that non-active surfaces must be electrically isolated from electrically conductive materials such as the saline solution on the exterior of the electrode, so that electrical conduction via these materials does not ground the circuit and prevent the electrode from delivering its current to the active surface. For example, wires or conducting materials that deliver current through the probe to the active surface need to be electrically isolated from the exterior of the probe, which can come into contact with body tissues during a procedure.
Much of the length of an electrosurgical probe is coated with an insulator or has lead wires that run inside insulated tubing. Near the active surface, however, insulating the electrodes becomes more difficult because of the extreme heat generated at the active surface. Many existing electrosurgical devices use an insulator such as a ceramic member to separate the active portion of the electrode from the remainder of the probe, both electrically and thermally. U.S. Pat. No. 7,244,256, to the present inventors and commonly assigned herewith, shows a preferred method of assembling an electrode to an electrosurgical probe using a ceramic insulating member; this technique can also be employed in manufacture of the improved electrode of the present invention.
It is also typical practice to construct the electrosurgical probe as a tubular member, so that a vacuum can be applied to the lumen of the probe to draw gasses, supplied fluid, ablated tissue, and other debris away from the surgical site. Typically the lumen communicates with the surgical site through an orifice in the electrode's active surface. In order that the ablated tissue and debris, which are typically entrained in a stream of saline solution provided for the purpose, are prevented from clogging the lumen of the probe, it is known to form the electrode's active surface such that the members providing the sharp edges that are preferred, as above, to ensure high current density are arranged to comprise a grate or filter. Larger particles of ablated tissue and debris are then caught on the active electrode surfaces of the filter and ablated into smaller particles, which can then be drawn past the active surfaces into the lumen.
For example, U.S. Pat. No. 7,150,746, also to the present inventors and commonly assigned herewith, shows the formation of the active surface of the electrode as a series of parallel rails, with the lumen of the probe in communication with the area under the active surface. This patent also teaches the provision of a further active edge at the lower end of the electrode for further ablating tissue particles that have passed through the filter provided by the outer electrode edges, to further reduce clogging of the opening of the lumen.
Despite these refinements, clogging of the lumen still occurs from time to time. The present invention is directed to further improvements in design of the electrode of electrosurgical probes, so as to further reduce clogging of the lumen of the probe by ablated tissue and other debris.